CAMBRIAN SYSTEM (CAMBRIAN ROCKS, ante), rocks belonging to the primordial division of palwozoic time, and comprising the oldest part of the lower Silurian age, appears on the American continent in Newfoundland, Nova Scotia, New Brunswick, Canada, northern New York, Vermont, eastern Massachusetts. the Appalachian moun tains, many parts of the Mississippi valley, and under the seeo•lary and younger palxo zoic rocks of the Rocky mountains. They are divided by American geologists into the Acadian and Potsdam groups: the former are the oldest of American primordial rocks, and contain a mass, 2000 ft. deep, of gray and dark shales with some sandstones; the latter, also in part sandstone, has iu Newfoundland a depth of 5600 ft., but in the val ley of the St. Lawrence diminishes to 600 and even 300 feet. The sandstone beds contain ripple marks, mud cracks, layers indicating the wind-drift, and ebb and flow structure, and animal tracks. The Acadian formation yields primordial trilobites of the genera
paradoxides conocoryphr, agnostus, and some others; brachiopods of the genera lingulella, (Mcina, obo.ella, and orthis; and several kinds of annelide tracks. The Potsdam rocks contain a few sponges, the earliest forms of graptolite, some brachiopods, including, besides the genera in the Acadian beds, obolus, camarella, and orthixina; some pteropods, (hyolites or theca); two species of orthoceras; annelide tracks; trilobites of the genera conocoryphe, agnostus, dikelocephalus, ptychaspis, chelriocephalus, aglavis, and ithrnurvs. Barrande found a remarkable uniformity in the organic remains of those parts of this system which be investigated, extending through Europe and America, and named by him the primordial zone.